Abstract Body (Do not enter title and authors here): Background:
Cardiopulmonary exercise testing (CPET) including measures of peak oxygen consumption (V_O2peak) and peak oxygen pulse (O_2pulse) is commonly used for adult congenital heart disease (ACHD) surveillance. However, less is known of the significance of the O_2pulse trajectory, which reflects the kinetics of stroke volume and peripheral oxygen extraction during exercise. The extent to which O_2pulse trajectory correlates with underlying anatomic complexity, New York Heart Association (NYHA) functional status, and cardiovascular function in ACHD patients remains unclear.

Objectives:
To assess the relationship between anatomic complexity, functional status, and cardiac function with O_2pulse trajectory in a heterogeneous ACHD population.

Methods:
We performed a single center retrospective analysis of ACHD patients who underwent CPET as part of their clinical evaluation. Demographics, clinical history, CPET data, and cardiac magnetic resonance imaging results were manually extracted from the medical record. Anatomic complexity was classified as simple, moderate, or great based on 2018 AHA/ACC guidelines. Functional status was determined using VO_2peak to estimate NYHA class equivalent. The O_2pulse trajectory was qualitatively defined as normal or abnormal (flat or decreasing). Data are presented as mean (SD) or number (%). Chi-square and analysis of variance was performed to compare O_2pulse trajectory groups.

Results:
A total of 223 ACHD patients (36 [12] years old, 55% female, 74% White race) had an evaluable O_2pulse trajectory. An abnormal O_2pulse trajectory (n=109 [49%]) was associated with increasing ACHD complexity (Figure 1; P=0.047) and NYHA classification (P=0.023).

Reductions in both right and left ventricular ejection fraction were associated with abnormal O_2pulse trajectory (RVEF: [normal vs abnormal trajectory]: 55 (10)% vs. 49 (14)%, P=0.001 & LVEF: 58 (8)% vs. 53 (9)%, P=0.002). Subjects with an abnormal O_2pulse trajectory demonstrated significantly greater right (but not left) ventricular end-diastolic and end-systolic indexed volumes (RVEDVI: 88 (31) mL vs. 109 (52) mL, P=0.004 & RVESVI: 40 (18) mL vs. 61 (44) mL, P<0.001).

Conclusions:
Greater anatomic complexity, higher NYHA classification, and worsening (right > left) ventricular function are associated with an abnormal O_2pulse trajectory in a heterogenous ACHD population. The clinical utility of this additional CPET parameter, reflecting O_2pulse kinetics, requires further study.